The brain show: viewing system provides surgical staff with front-row seats.

The surgical suite is not the roomiest shop floor for working. It's not intended to be--most procedures are on a single region of the patient, precluding need for excess movement. To serve the surgeon and staff, the remaining floor space is taken up by equipment trays and support systems, like the anesthesia cart.

There are some surgeries, however, that require the active participation of more than one surgeon. The difficulty increases further when the procedure involves microsurgery, and the field of operation is reduced to the area seen through a microscope. More and more procedures are being handled through image-guided surgery, including various brain surgery approaches, particularly planning the craniotomy, navigation in deep seated tumors, skull base surgery and acoustic neuromas. In the spine, image-guided surgery has been used in the placement of pedicle screws, lateral mass screws and transarticular C1-2 screws. The result is that the reduced invasiveness in turn reduces the recovery time for the patient. Many return home the same day.

Computers in surgery

Image-guided surgery developed from the idea that a computer could be employed to track a surgical instrument during a procedure, constantly representing the tool's position relative to diagnostic images stored in the computer's database. It serves as a confirmation to surgeons in the case of abnormal anatomy, undifferentiated tumors, or tumors located in critical areas (e.g. near the motor cortex). During the operation, the surgeon uses instruments connected to the position sensor to view the images at the location that he is touching. For example, during a brain operation, the surgeon may wish to confirm that a structure is part of the tumor he is trying to remove. He will touch the pointer to the anatomy in question in the patient's brain and examine the system screen. Crosshairs will be shown on the image corresponding to the location that the surgeon is touching.

Another aspect being explored in image-guided surgery comes from the issue that while a patient's skull may be rigidly clamped, the brain tissue is a non-rigid mass. Systems that rely on the assumption that a pre-operative MR image accurately reflects the shape of the brain during surgery are insufficient for a broad range of neurosurgical tasks. Techniques are being developed that use ultrasound images of the brain, collected during the surgery, to track the distortion of the brain tissue. Once the distortion has been measured, it is used to warp the pre-operative MR images such that they accurately reflect the shape of the brain during surgery.

Additionally, image-guided surgery is used as a targeting and control tool to provide focused radiology treatments with pinpoint accuracy. With this navigation technology functioning like a GPS system, target volumes of tumors can be localized with great accuracy, allowing surgeons to attack the tumor with high-precision radiation.

Correlation

At the beginning of image-guided brain surgery, the first and most critical task is to create an alignment between the diagnostic information and the living patient. Several systems use small markers, called fiducials, which are placed directly onto the patient's head prior to having pre-surgery MRI and CAT scan. Leaving the fiducials in place provides guideposts for the computer system during the surgery. Another version, developed by BrainLAB Inc., Redwood City, CA, uses a non-contact system employing two IR emitter/detectors and a class 1 laser wand to create an array of surface points on the patient's face and/or head The feature recognition software in the system then matches the registration.

An integrated suite

BrainLAB's registration device, known as Z-Touch, is a component in a larger system developed by the company. Called BrainSUITE, it is an integration of image-guided surgery, an MRI system, and visualization and data management technology in a surgical theater.

As is necessary in brain surgery, BrainSUITE provides a microscope. It's equipped with a video camera to share data, as well as to record procedures for later review and training. The microscope, a Zeiss OPMI NC 4 Multivision, also contains a microdisplay system for color images such as navigational overlays and other data that can be projected into the microscope image, further improving the surgeon's efficiency. A glass panel measuring 3.6- x 13.2-ft is inset into one wall of the surgical suite, and diagnostic scans, live video, and navigation views are rear-projected onto the panel to support surgical decision making, while providing an additional teaching aid. Since the glass panel is the only part of the projection system that enters the surgical space, sterilization and EMI concerns are minimized.

The surgeon has another display near to hand, with a touchscreen that permits control of the operative environment. From here, OR functions including IGS controls, lighting, data on the viewing wall and room temperature are easily adjusted.

The MRI system, developed around a Siemens Magnetom 1.5 Tesla unit, provides imaging immediately before surgery begins to allow compensation for any changes that may have occurred since diagnostic imaging. After being brought into the operating room, the patient is scanned and the images are immediately loaded into the VectorVision database. This integration assists in patient registration and immediately updates images in the IGS system. During the course of the procedure the patient can be re-scanned at any time in order to update information and provide the surgeon with the latest information for the surgical procedure. An "image compare mode" allows the surgeon to visualize and verify surgical progress. A final scan can be made, prior to closing the patient, to further reduce the risk of recurrence and re-operation.

The placement of the MRI coil in the surgical suite posed unique problems for personnel regarding both proximity and exposure, and proximity to equipment that could not be rendered non-magnetic. To resolve these, an OR table was designed that would keep the skull outside the 5 Gauss line from the coil, yet pivot smoothly around a knee-level axis when an MRI was required. The table has additional pitch, roll and tilt axes, so imaging is not limited in angle of view. Additionally, having instruments on rolling trays and other apparatus suspended from the ceiling permits removal of equipment further outside the zone where the magnetic fields of the scan might be affected.

By approaching the creation of a surgical space as a sqystems integration project, BrainLAB has assembled a work area relatively free of clutter, and nearly ready to go "out-of-the-box." The suspension of support systems from the ceiling removes many power and interfacing data cables, and the consistent use of specific vendors provides assurance that the suite is debugged before surgery begins.

Which, no doubt, would come as good news to the patient.

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